Monday, May 12, 2008
No Torque Please
In physics, a torque (τ) is a vector that measures the tendency of a force to rotate an object about some axis (center). The magnitude of a torque is defined as force times the length of the lever arm. In plain weightlifting english, the further away the object that you are trying to lift is from your body, the less effective you are going to be at lifting that object straight up. Because, the further the bar is from your body, the more your energy has to go into resisting the torque being generated by you. Not only do you have to expend energy to remain upright, but with the bar out past your feet you've got to change the force vector of your jump, pull, or push, and you've effectively limited the potential of your own body's leverage. Buzz kill.
Note that in the photo of Olliver above, the bar has brushed up his shirt after his second pull. Obviously he has figured out that the closer that he can keep that bar to his body, the more effective he is going to be generating vertical force. The shirt lift is a nice cue and easy to spot in a very quick lift like the clean or snatch.
Now on to the nitpick. Note that while Olli is hitting excellent full extension and that the bar is caught in his shirt, there is still some distance between his stomach and the weight. The distance between the two is the lever arm or moment arm. Remember our physics above? Doubling the distance between the stomach and the bar doubles the effective length of the lever and doubles the torque. So now it is twice as hard to resist getting pulled forward onto your toes into the dreaded "poo position." Note also that Olli isn't actually jumping straight up, but that he's actually jumping backward (slight body lean) a little to compensate for the fact that he has to adjust for the bar being a few extra inches from his skin. Olli is trapped. He has to give away some of his hard earned vertical force for a little counter balance back lean force. And, you can bet your sweet self that Andrew Henry is going to try and exploit this small inefficiency. Two inches of extra torque is two too many.
Keep it close, and keep the torque down. Please.
Coach moment about the axis-star.
at 10:23 PM